The present invention relates to an inner rotor type brushless motor.
For example, Japanese Patent No. 2875497 discloses an inner rotor type brushless motor that includes a stator core.
The stator core is formed by laminating several core sheets. Each core sheet is formed by punching a magnetic metal plate. The stator core includes a ring-shaped outer core, a ring-shaped inner core, and teeth, which extend straight in the radial direction. A coil is wound about the teeth. The teeth are arranged along the circumferential direction of the stator core at equal angular intervals about the axis of the stator core. The radially inward end of each tooth extends from the inner core. The inner core has a rotor accommodating hole for accommodating a rotor. The radially outward end of each tooth is coupled with the inner circumferential portion of the outer core. In the case with the stator core of the publication, the coil can be wound about the teeth before coupling the outer core with the inner core.
A stator, which is formed by winding the coil to the above mentioned stator core, is inserted into a motor housing and fixed to the inner circumferential surface of the motor housing.
The above mentioned brushless motor has a rotational sensor, which detects the rotational position of the rotor. The rotational sensor is used to obtain a drive current suitable for generating a rotating magnetic field on the stator. The position of a rotating portion of the rotational sensor is determined with respect to the rotor in the circumferential direction of the stator such that the rotational sensor accurately detects the rotational position of the rotor. Further, the position of a fixed portion of the rotational sensor is determined with respect to the stator in the circumferential direction of the stator and then fixed to the motor housing.
Accordingly, a brushless motor that includes a positioning groove and a positioning projection has been proposed. The positioning groove is formed in the outer circumferential surface of the stator, that is, the outer circumferential surface of the outer core. The positioning groove is located at a substantial center between the adjacent teeth. The positioning groove extends in the axial direction of the stator. The positioning projection, which fits with the positioning groove, is formed in the inner circumferential surface of the motor housing. The circumferential width of the positioning groove and the circumferential width of the positioning projection are substantially the same, or the circumferential width of the positioning groove is slightly less than the circumferential width of the positioning projection so that the stator is firmly secured to the motor housing without any play in the circumferential direction.
When fitting the positioning projection to the positioning groove, a load is applied to the positioning groove of the outer core. The load is likely to cause distortion and deformation of the outer core.
The distortion and deformation of the outer core adversely affects the inner core and could reduce the circularity of the rotor accommodating hole. If the circularity of the rotor accommodating hole decreases, the size of the space between the stator and the rotor is changed. This decreases output of the motor, or increases vibration generated during rotation of the motor.
Each tooth extends straight in the radial direction. Each tooth and the outer core are coupled at a right angle. In other words, a joint portion between each tooth and the outer core is not smooth. Therefore, the magnetic path is bent at substantially the right angle at the joint portion between each tooth and the outer core, which increases the magnetic resistance. As a result, the performance of the motor is decreased.
Accordingly, it is an objective of the present invention to provide a brushless motor that is not likely to cause distortion and deformation of a stator and has an improved performance.
To achieve the above objective, the present invention provides a brushless motor, which includes a cylindrical motor housing, a stator, a fitting portion, and a fitted portion. The stator is fitted in the motor housing and includes a ring-shaped outer core and teeth, which extend in the radial direction of the stator. Each tooth has a radially outward end and a radially inward end. The radially outward end of each tooth is coupled with the outer core. Each tooth has a predetermined width in the circumferential direction of the stator. The fitting portion is located on the inner circumferential surface of the motor housing. The fitted portion is located on the outer circumferential surface of the outer core. The fitted portion is arranged on a radial line that passes through the center of the width direction of one of the teeth. The fitting portion is fitted to the fitted portion to determine the position of the stator with respect to the motor housing in the circumferential direction.
The present invention also provides a brushless motor. The brushless motor has a cylindrical motor housing, a stator, a plurality of coupling portions and a plurality of wide portions. The stator is secured to the inside of the motor housing. The stator includes a ring-shaped outer core, and a plurality of teeth, which are coupled with the outer core and extend in the radial direction of the stator. Each tooth has a radially outward end and a radially inward end. Each tooth has a predetermined width in the circumferential direction of the stator. The coupling portions, each of which corresponds to one of the teeth and is located between one of the corresponding tooth and the outer core. Each coupling portion couples the radially outward end of the corresponding tooth with the outer core. The circumferential width of each wide portion is greater than the width of a portion of each tooth other than where the corresponding coupling portion is formed.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.